Nikki can certainly speak eloquently to this if she chooses, but in speaking of her concerns at length in some of her past posts, her main issue seemed to be the nature of the attack of tube amps vs Axe Fx. While he wasn't expansive in the thread, there was a response from Cliff in one of those threads responding to her where he says something like "don't let the perfect be the enemy of the good." To my ear he was conceding that the nature of the beast is such that the conversion process and the input does do something to the attack which isn't replicating tube amp behavior exactly. Being the inquisitive explorer that she is, Nikki pressed him on the exact nature of the difference, but he didn't want to go there and that's where they left it.
The difference in attack behavior is a make or break difference for her choosing only to use the Axe II for effects and not for amp sounds as well. For most here, including me, that difference either isn't perceived or isn't a deal breaker. For me, it's the later. With older modelers like POD/POD2, it was almost like the attack was encased in aural plastic - nothing like a real amp. With the Axe I do hear a tiny trace of that characteristic, but it's followed by so much dialability that I still feel I get more expressiveness out of the attack on the Axe II than I do with my tube amps/pedals except under their absolute optimum operating conditions, and even then the current Axe II sound is right there with the tube rig to my ear.
